All posts tagged 400 ppm CO2

If you’re a regular reader of this blog and its comments section, you’re probably more than a little worried about two bits of climate science in particular:

Our understanding of past climates (paleoclimate) and 5-6 C long term climate sensitivity.

And if you’re a frequent returner, you’ve probably figured out by now that the two go hand in glove.

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Looking back to a period of time called the Pliocene climate epoch of 2.6 to 5.3 million years ago, we find that atmospheric carbon dioxide levels were somewhat lower than they are at present — ranging from 390 to 400 parts per million. We also find that global temperatures were between 2 to 3 degrees Celsius warmer than 1880s ranges, that glaciers in Antarctica and Greenland were significantly reduced, and that sea levels were about 25 meters (82 feet) higher than they are today.

(The Totten Glacier is one of many Antarctic land ice systems that are under threat of melt due to human-forced warming. A new paleoclimate study has recently found that levels of atmospheric greenhouse gasses that are below those presently in our atmosphere caused substantial Antarctic melt 4.23 million years ago. Image source: antarctica.gov.)

Given that atmospheric CO2 levels during 2017 will average around 407 parts per million, given that these levels are above those when sea levels were considerably higher than today, and given that these levels of heat trapping gasses are rapidly rising due to continued fossil fuel burning, both the present level of greenhouse gasses in the Earth’s atmosphere and our understanding of past climates should give us substantial cause for concern.

This past week, even more fuel was thrown onto the fire as a paleoclimate-based model study led by Nick Golledge has found that under 400 parts per million CO2 heat forcing during the Pliocene, substantial portions of Antarctica melted over a rather brief period of decades and centuries.

Notably, the model found that the West Antarctic Ice Sheet collapsed in just 100-300 years under the steady 400 ppm CO2 forcing at 4.23 million years ago. In addition, the Wilkes Basin section of Antarctica collapsed within 1-2 thousand years under a similar heat forcing. In total, the study found that Antarctica contributed to 8.6 meters of sea level rise at the time due to the loss of these large formations of land ice.

We conclude that the Antarctic ice sheet contributed 8.6 ± 2.8 m to global sea level at this time, under an atmospheric CO2concentration identical to present (400 ppm). Warmer-than-present ocean temperatures led to the collapse of West Antarctica over centuries, whereas higher air temperatures initiated surface melting in parts of East Antarctica that over one to two millennia led to lowering of the ice-sheet surface, flotation of grounded margins in some areas, and retreat of the ice sheet into the Wilkes Subglacial Basin. The results show that regional variations in climate, ice-sheet geometry, and topography produce long-term sea-level contributions that are non-linear with respect to the applied forcings, and which under certain conditions exhibit threshold behaviour associated with behavioural tipping points (emphasis added).

This study began the publication process in 2016 when year-end atmospheric CO2 averages hit around 405 parts per million. By end 2017, those averages will be in the range of 407 parts per million. Even more worrying is the fact that CO2 equivalent forcing from all the various greenhouse gasses that fossil fuel burning and related industrial activity has pumped into the atmosphere (methane, nitrogen oxides, CFCs and others) will, by end 2017 hit around 492 ppm.

As a result, though conditions in Antarctica are presently cooler than during 4.23 million years ago, the considerably higher atmospheric greenhouse gas loading implies that there’s quite a lot more warming in store for both Antarctica and the rest of the world. A warming that, even if atmospheric greenhouse gasses remain at present highly elevated levels and do not continue to rise, could bring about a substantially more significant and rapid melt than during the Pliocene.

The truth is, when I was born, atmospheric CO2 levels were around 300 ppm. Today — maybe even this week — will be the last time anyone alive experiences a level below 400 ppm, and no one born in the coming century or even longer will ever see less than 400 ppm again. That is a deep, deep observation, with ramifications for our children and for every future generation. — Peter Gleick during November of 2015

I just want to take a moment to tell you something that’s pretty important. You are now an alien. You’ve been made an alien by fossil fuel burning. And you’re now living in, breathing, a heat-trapping atmosphere that’s entirely alien to your species. Sometimes races of creatures suffering such habitat changes are capable of surviving the environmental shifts that inevitably occur as a result. Sometimes they are not. But you’ve been placed in this situation now and it’s getting steadily worse.

Big August CO2 Jump Locking 400 ppm In

The August preliminary data are in. And it’s pretty grim. For with a big year-on-year CO2 jump in August, it looks like September of 2016 will be unable to achieve monthly CO2 averages below 400 parts per million. What that means is that the last month below the 400 level was probably October of 2015. So, for almost a year now, we’ve been living in the climate age of 400+, likely never to return to monthly atmospheric CO2 levels in the 300s again during the lifetimes of any of us humans now inhabiting this Earth.

According to NOAA, August CO2 measurements at the Mauna Loa Observatory averaged 402.25 parts per million, which is a big 3.32 parts per million jump over 2015 August readings. Adding this number to previous months, we find that 2016, so far, has seen an average rate of rise of 3.495 parts per million during its first 8 months — significantly ahead of previous annual record rates of rise during 2015 and 1998 (3.05 and 2.93 ppm respectively).

(Two year Keeling Curve trend seems to indicate that it’s unlikely monthly values will fall below 400 parts per million during 2016 and, for all practical purposes, ever again unless some kind of unprecedented change is made to global carbon emissions policies. Image source: The Keeling Curve.)

Such a big August jump makes it highly unlikely that September will average below 400 parts per million due to the fact that monthly drops leading into September typically average around 1.8 ppm CO2. If this trend holds true for 2016, then September will average around 400.5 ppm CO2. And since September typically sees the lowest atmospheric CO2 levels during any given year, the current month is basically the world’s last chance to see a 30 day period that averages below 400 ppm.

Conditions Not Seen in Millions of Years

Atmospheric CO2 levels are now so high that you have to go back about 3 million years into the Pliocene to find similar ranges. During that time, the world was between 2 and 3 degrees Celsius warmer than 1880s temperatures. Oceans were 25 to 75 feet higher and the world was a dramatically different place.

(The age of 400 parts per million CO2 is here. It’s something not seen in about 3 million years. In other words, you’re breathing air right now composed of properties that no homo sapiens sapiens has ever breathed before. Image source: Climate Central.)

But adding in all greenhouse gasses like Nitrogen compounds and Methane resulting from fossil fuel burning (and other human activities) and you end up with a CO2 equivalent in the atmosphere close to 490 parts per million. Such a level of forcing correlates more closely to an even more ancient climate period called the Middle Miocene of about 15 million years ago when global temperatures were between 3 and 4 C warmer than they are today.

As such, crossing the 400 ppm CO2 threshold is not merely symbolic. It is a sign of the increasing likelihood of climate harms to come. And it appears now that we crossed that pass back during October of 2015 — unaware that we’d already entered a tough new climate age.

There’s a tale in the ice. A record of past atmospheres locked away as snowfall trapped air bubbles and then compressed them into thin layers age after age over tens of thousands of years. Over the last few decades, scientists have been drilling holes in the great ice packs of Greenland and Antarctica. Their quest? To unlock this tale and reveal a direct record of global greenhouse gas levels through the deep past.

What their drilling uncovered was both quite informative and rather chilling. First, it showed that, for more than 800,000 years, global CO2 levels had been relatively stable in a range of 180 to 300 parts per million. As the levels of heat trapping CO2 rose, temperatures peaked during brief interglacials. And as levels fell, temperatures plunged back into ice age conditions.

Global temperature flux during these swings from ice age to interglacial were just 4 degrees Celsius. A 100 ppm CO2 rise correlated roughly to a 250 foot rise in sea level and much warmer average conditions globally. A corresponding fall of about the same amount brought temperatures back down and piled ice two miles high over today’s temperate regions such as New York.

What the ice cores also revealed was that human CO2 emissions had pushed global levels of this potent greenhouse gas far out of any climate reckoning comparable to the context of human beings, who have only existed in current form for about 200,000 years.

In fact, what scientists found was that atmospheric CO2 levels were pushing more than 100 parts per million higher than at any time during this vast epochal span:

(Antarctic ice core CO2 record and comparable temperature swings. Note that the difference between ice age and interglacial is about 8 C of local temperature and about 100 ppm of CO2. It is worth considering that, due to polar amplification, Antarctic temperature changes were about double the global average. Current CO2 levels are more than 100 parts per million higher than even the peak value over this 800,000 year period. If an average peak interglacial CO2 average of 275 ppm is considered, then current values are around 127 parts per million higher. Image credit: Havard/Jeremy Shakun.)

This record was a key contribution to climate science. One, it revealed how past CO2 levels compared to past temperatures. And since the data was directly derived from air bubbles trapped beneath hundreds of feet of ice, it also provided us with an exact measure for past atmospheres.

Secondly, and perhaps much more ominously, it showed us how very far beyond any climate comparable to that great span of time we’d already come.

102 ppm higher than at any time in the last 800,000 years

Humans have now pushed the CO2 boundary 102 parts per million higher than the context provided by the last 800,000 years. It’s kind of a big deal when you consider that a mere fluctuation of about 100 parts per million CO2 was enough, when combined with changes in orbital forcing, to set off feedbacks resulting in a 4 C temperature change globally (8 C change for the Antarctic environment) as ice age proceeded to interglacial and back.

Current human forcings through CO2 and other emissions have now entirely over-ridden the natural cycle, eliminating the possibility for future ice ages and putting us on a trajectory for catastrophe. With annual global carbon emissions now exceeding 12 gigatons, not only have we forced ourselves well outside of any past bounds to which we can easily relate, we have also generated an unprecedented velocity of change. For the current human carbon emission now exceeds, by at least six times, the most rapid past level of natural carbon emission.

No vast flood basalt could ever rival the volume and pace at which humans currently emit greenhouse gasses.

This enormous emission continues to have severe effect through an ever-higher ratcheting of global CO2 levels.

As of the past week, global daily CO2 values had rocketed to 402.2 parts per million, well outside anything seen in the ice core record:

(Mauna Loa Observatory CO2 measure for the last six months. Note that daily and weekly values have been mostly above 400 ppm since early March. Image source: The Keeling Curve.)

This an extraordinary measure. One that has no context in direct records such as those available to us through ice core data. But paleoclimate proxy data does provide some corollary. According to isotopic carbon measures found through seabed samples, we can determine that the last time CO2 levels were above 400 parts per million was during the mid-Plieocene between 3 and 3.3 million years ago.

And during that time global average temperatures were 2 to 3 degrees Celsius warmer than they are today (with Antarctic values at least twice that). Both Greenland and West Antarctica were mostly ice free and sea levels were between 15-75 feet higher. These are, likely, the potential low end of the changes we’ve locked in due to human global greenhouse gas forcing long term, even if, somehow, global CO2 levels are brought to a plateau.

(An graphic extrapolation of Antarctica’s ice cover and elevation based on paleoclimate data. Note that the Antarctic ice sheet is greatly diminished at a time when CO2 values remained constant around 400 ppm. Image source: Commons.)

480 CO2e…

Unfortunately, the global CO2 measure doesn’t tell quite the entire story. For atmospheric levels of gasses like methane, nitrous oxide, and a host of less common industrial chemicals have also all been on the rise in Earth’s atmosphere due to human emissions. As a result, according to research by the Advanced Global Atmospheric Gasses Center at MIT, total heat forcing equal to CO2 when all the other gasses were added in was about 478 ppm CO2e during the spring of 2013. Adding in the high-velocity human greenhouse gas contributions since that time gets us to around 480 ppm CO2e value. In the context of past climates and of near and long term climate changes due to human interference, 480 ppm CO2e is nothing short of fearsome.

The last time the world saw such a measure of comparable atmospheric greenhouse gas heat forcing was during the Miocene around 15-20 million years ago. At that time, global temperatures were 3-4 C warmer, the Antarctic ice sheet was even further diminished, and sea levels were 80-120 higher than today.

This combined forcing is enough to result in a state of current climate emergency. In just a few years, according to the recent work of climate scientist Michael Mann, we will likely lock in a 2 C short term warming this century and a probable 4 C warming long-term. If the current, high-velocity pace of emission continues, we will likely hit 2 C warming by 2036, setting off extraordinary and severe global changes over a very short period.

These are very dangerous and, likely, catastrophic levels. In such a context, the inexorably rising rate of atmospheric CO2 and other greenhouse gas forcings simply adds further insult to a very high risk situation.

According to reports from The Mauna Loa Observatory and The Keeling Curve, daily CO2 values for March 12 rocketed to a record 401.6 parts per million. Hourly values rose briefly higher, touching 402 parts per million. Levels fell back to around 400 ppm on March 13. But the overall trend will continue upward through March, April and much of May when the height of annual atmospheric CO2 readings is typically reached.

By comparison, during May of last year, daily and weekly values hit just slightly higher than 400 parts per million while measures for the month hovered just below this number. We are now about two months away from the 2014 peak. So it appears possible that daily values could rise to 404 ppm or greater with highs for the month potentially exceeding 402 ppm (you can view a comparison graph for May 2013 here).

(Daily and hourly atmospheric CO2 values from March 7 to 13. Image source: The Keeling Curve.)

Such high levels of this gas have not been seen on Earth in over 3 million years. A time when temperatures were 2-3 degrees Celsius warmer and sea levels were 15-75 feet higher than today. And should CO2 levels merely remain at the level currently achieved, we can probably expect at least the same amount of warming long-term.

CO2 in Context

Annually, the average rate of CO2 increase now is an extraordinary 2.2 parts per million each year. This rate is about 6-7 times faster than at any time in geological history. None of the vast flood basalts of the ancient past, no period of natural vulcanism, can now rival the constant and massive injection of this powerful and long-lasting greenhouse gas by humans into the atmosphere.

Last year, the rate of increase spiked to around 2.5 parts per million and we can view this as mere prelude under a continuation of business as usual. For if human fossil fuel emissions are not radically brought into check, the ongoing economic inertia of existing fossil fuel based infrastructure and planned new projects will likely shove this rate of increase to 3, 4 even 7 parts per million each year by the end of this century. As a result, CO2 levels alone have the potential to reach catastrophic values of 550 parts per million by around 2050-2060 that, long term and without any of the added effects of other greenhouse gasses, would be enough to eventually melt all the ice on Earth and raise global temperatures to around 5-6 degrees Celsius above current levels. A level that, through acidification alone and not including damage through stratification and anoxia, could drive up to 1/3 of ocean species to extinction.

CO2 accounts for much of the greenhouse forcing when taking into account the feedbacks it produces on water vapor and clouds. NASA notes:

Because carbon dioxide accounts for 80% of the non-condensing GHG forcing in the current climate atmosphere, atmospheric carbon dioxide therefore qualifies as the principal control knob that governs the temperature of Earth.

All other greenhouse gasses pale in comparison to both its total effect and its current rate of increase. Methane, the next most potent greenhouse gas, accounts for about 15% of the forcing and is rising at a rate of 4 parts per billion (1/550 that of CO2), generating a net effect equal to, in the worst case, an additional .4 parts per million CO2 each year (.29 when aerosols drop out). A troubling and dangerous increase itself. But still a mere shadow compared to the overall rate of CO2 increase.

CO2 is also the longest lived of the major greenhouse gasses with one molecule of CO2 providing effective atmospheric warming for at least 500 years. By comparison, the oxidation time for a single molecule of methane is around 8 years. What this means is that it takes an ever increasing methane emission just to keep values constant while atmospheric CO2 takes much longer to level off given even a constant rate of emission.

The result is that heat forcing from CO2 tends to remain constant over long periods while methane heat forcing values have a tendency to spike due to rapid oxidation.

(Radiative forcing from a 10 gigaton release of methane in red compared to expected end century CO2 values of 750 ppm. Note how the methane heat forcing spikes and then rapidly falls off. Image source: RealClimate.)

Current rates of CO2 increase, therefore, should be viewed as catastrophic to climates that are both livable and benevolent to humans. A rate of increase that puts at risk severe changes to Earth environments and which provides a trigger for setting off a series of powerful amplifying feedbacks through the medium and long term. These include both loss of ice albedo and the potential for spiking methane emissions from the widespread natural store.

UPDATE:

Most recent daily values from March 12 onward in relationship to the six month trend. Note the sharp spike upward at the end of the period as well as the overall volatility of the trend line. High volatility may well be an indication that the typical carbon cycle is suffering disruption with sinks, stores and sources experiencing larger than typical fluxes.

According to the most recent report from the Mauna Loa Observatory, world CO2 concentrations reached a record 396.8 PPM in February.

Considering that we have three more months of seasonally increasing world CO2 values, it is possible that 2013 will see CO2 levels break 400 PPM for the first time in at least 3 million years.

The last time CO2 levels were this high was during the Pliocene epoc. This geological period, occurring about 2.5-5.3 million years ago, exhibited CO2 averages in the range of 365 to 410 ppm.

During the Pliocene, no ice covered Greenland or West Antarctica. Sea levels during the Pliocene were about 75 feet higher than they are today.

For February 2013, world CO2 levels were 3.26 PPM higher than CO2 levels in February of 2012. On average, world CO2 levels are increasing at a rate of 2.2 parts per million each year (but ramping higher). At this rate of increase, it will be less than five years before world CO2 levels exceed that of the Pliocene and begin to enter a range prevalent during the Miocene of around 400-600 ppm CO2.

Early Miocene was a time when no glaciers covered the poles. So pushing world CO2 values out of the range of the Pliocene and into that of the Miocene presents a serious amplification of already challenging climate difficulties.